“Everyone thinks he talks a lot, but I don’t see a problem,” 49ers cornerback Tramaine Brock said. “He shows up when he talks.”

Who will show up among the 49ers’ ever-changing, often-quiet cornerback corps when they visit Seattle on Sunday, with playoff implications in the brisk air? Do the 49ers have a cornerback capable of making a Sherman-like impact or even a game-changing play?

“It’s a tough environment, but we’ve just got to play ball,” right cornerback Chris Culliver said. “We’ve got to play San Francisco 49er ball and just win the game.”

The 49ers (7-6) have lost their past two games, starting with a 19-3 blowout to the Seahawks on Thanksgiving and then a 24-13 upset at the Raiders last Sunday.

Injuries and absences have hit the 49ers defense hard all season, and that’s no different for their cornerback corps, which called up Marcus Cromartie from the practice squad Sunday. In other moves, the 49ers put linebacker NaVorro Bowman and nose tackle Glenn Dorsey on season-ending injured reserve while also promoting guard Andrew Tiller from the practice squad.

Cromartie’s arrival could signal the unavailability Sunday of Culliver (knee) along with Brock (hamstring). Culliver is listed as questionable after leaving the loss to the Raiders with a left knee injury. He has started all but one game this season after missing 2013 because of a torn anterior cruciate ligament in his left knee. Culliver has battled general soreness in that knee with what he terms constant maintenance.

“I felt it would be a test year because I’ve never had this type of injury,” Culliver said.

Brock, as has been the case most of this season, is not expected to play, as a hamstring strain is preventing him from running at full speed. After breaking out last season to earn a three-year extension, Brock hasn’t started since the season opener because of toe, ankle and hamstring injuries.

“It’s been terrible. I’ve been hurt and couldn’t get back out there,” Brock said.

If Culliver and Perrish Cox start, it will be rookie Dontae Johnson again at nickel back, with practice-squad call-up Leon McFadden the dime back.

Johnson was thrust into action after injuries took down Brock, Chris Cook and Jimmie Ward, this year’s first-round draft pick who was the nickel back before reinjuring his foot Nov. 9 at New Orleans. Cook bowed out with a season-ending hamstring tear Oct. 19.

A constant in Seattle’s lineup has been Sherman, who has only three interceptions all season but hasn’t allowed a completion in the past three games (all wins).

“He’s fast. He’s long. He does a great job covering guys,” 49ers quarterback Colin Kaepernick said. “So, he makes the windows very small for being able to get the ball into receivers.”

In the 49ers’ last game in Seattle, Sherman’s end-zone pass breakup set up an interception that sealed the Seahawks’ NFC Championship game win. Then came his two interceptions in a Thanksgiving night rout. His mouth took center stage after both wins, from roaring taunts into a postgame microphone at the NFC title game to eating turkey on the 49ers’ midfield logo two weeks ago.

“It worked out for him,” 49ers right tackle Anthony Davis said of Sherman, who signed a contract extension (four years, $56 million) in May. “He got paid a lot of money. Good for him.”

Culliver and Cox are pending free agents, so the 49ers’ cornerback corps could be overhauled for a second consecutive offseason. Carlos Rogers and Tarell Brown were three-year starters before leaving last offseason for the Raiders.

“If it was up to me, I’d like them to stay here,” Johnson said of Culliver and Cox. “I’ve learned a lot from those guys. But that’s out of my hands, and my focus is on preparation, week in and week out.”

“Everyone thinks he talks a lot, but I don’t see a problem,” 49ers cornerback Tramaine Brock said. “He shows up when he talks.”

Who will show up among the 49ers’ ever-changing, often-quiet cornerback corps when they visit Seattle on Sunday, with playoff implications in the brisk air? Do the 49ers have a cornerback capable of making a Sherman-like impact or even a game-changing play?

“It’s a tough environment, but we’ve just got to play ball,” right cornerback Chris Culliver said. “We’ve got to play San Francisco 49er ball and just win the game.”

The 49ers (7-6) have lost their past two games, starting with a 19-3 blowout to the Seahawks on Thanksgiving and then a 24-13 upset at the Raiders last Sunday.

Injuries and absences have hit the 49ers defense hard all season, and that’s no different for their cornerback corps, which called up Marcus Cromartie from the practice squad Sunday. In other moves, the 49ers put linebacker NaVorro Bowman and nose tackle Glenn Dorsey on season-ending injured reserve while also promoting guard Andrew Tiller from the practice squad.

Cromartie’s arrival could signal the unavailability Sunday of Culliver (knee) along with Brock (hamstring). Culliver is listed as questionable after leaving the loss to the Raiders with a left knee injury. He has started all but one game this season after missing 2013 because of a torn anterior cruciate ligament in his left knee. Culliver has battled general soreness in that knee with what he terms constant maintenance.

“I felt it would be a test year because I’ve never had this type of injury,” Culliver said.

Brock, as has been the case most of this season, is not expected to play, as a hamstring strain is preventing him from running at full speed. After breaking out last season to earn a three-year extension, Brock hasn’t started since the season opener because of toe, ankle and hamstring injuries.

“It’s been terrible. I’ve been hurt and couldn’t get back out there,” Brock said.

If Culliver and Perrish Cox start, it will be rookie Dontae Johnson again at nickel back, with practice-squad call-up Leon McFadden the dime back.

Johnson was thrust into action after injuries took down Brock, Chris Cook and Jimmie Ward, this year’s first-round draft pick who was the nickel back before reinjuring his foot Nov. 9 at New Orleans. Cook bowed out with a season-ending hamstring tear Oct. 19.

A constant in Seattle’s lineup has been Sherman, who has only three interceptions all season but hasn’t allowed a completion in the past three games (all wins).

“He’s fast. He’s long. He does a great job covering guys,” 49ers quarterback Colin Kaepernick said. “So, he makes the windows very small for being able to get the ball into receivers.”

In the 49ers’ last game in Seattle, Sherman’s end-zone pass breakup set up an interception that sealed the Seahawks’ NFC Championship game win. Then came his two interceptions in a Thanksgiving night rout. His mouth took center stage after both wins, from roaring taunts into a postgame microphone at the NFC title game to eating turkey on the 49ers’ midfield logo two weeks ago.

“It worked out for him,” 49ers right tackle Anthony Davis said of Sherman, who signed a contract extension (four years, $56 million) in May. “He got paid a lot of money. Good for him.”

Culliver and Cox are pending free agents, so the 49ers’ cornerback corps could be overhauled for a second consecutive offseason. Carlos Rogers and Tarell Brown were three-year starters before leaving last offseason for the Raiders.

“If it was up to me, I’d like them to stay here,” Johnson said of Culliver and Cox. “I’ve learned a lot from those guys. But that’s out of my hands, and my focus is on preparation, week in and week out.”